Treatment of benzene hexachloride



March 11, 1958 J. c HE'rRlcK 2,825,616

TREATMENT oF BENZENE HEXACHLORIDE Filed Nov. 8, 1954 $507 HSWOS/ VWWVS Z S'SJJXS IVVENTO.

'JAMES C. HE THICK BY/ 7 E ATTORNEY United States Patent Ov TREATMENT OF BENZENE HEXACHLRIDE James C. Hetrick, Berkley, Mich., assigner to Ethyl Corporation, New York, N. Y., a corporation of Delaware Application November 8, 1954, Serial No. 467,610

2 Claims. (Cl. 260-648) This invention relates to the treatment of a mixture of benzene hexachloride isomers to enhance the gamma isomer concentration therein, and more particularly to a method for extracting the gamma isomer from crude BHC and thereafter crystallizing an enriched gamma isomer fraction therefrom. This application is a continuation-in-part of my copending applications Serial No. 287,019, tiled May 9, 1952, and Serial No. 287,020, filed May 9, 1952, both now abandoned.

It is known that benzene hexachloride (ll,2,3,4,5,6 hexachlorocyclohexane), frequently called BHC, occurs in a number of isomeric forms. For example, in the addition chlorination of benzene, at least five such isomers are formed having approximately the weight distribution: a, 65 percent; 8 percent; fy, 13 percent; l percent; e, less than l percent; and the remainder, heptachlorocyclohexane and otherA impurities. It is also known that the gamma isomer is by far the most insee* ticidally active isomer. Accordingly, it is desired to concentrate isomer mixtures with respect to the gamma isomer to facilitate the preparation of improved insecticidal formulations by the elimination of the inert isou mers and odorferous constituents thereof.

Prior methods have been disclosed for concentrating the gamma isomer in isomer mixtures by extraction and fractional crystallization. ln the extraction step, a solvent is employed having a limited solubility for the a and ,8 isomers, and thus large quantities of these isomers may be separated from the saturated gamma-containing extract. For example, when extracting a crude benzene hexachloride isomer mixture having the composition noted above with lower aliphatic alcohols, an extract is obtained having approximately six parts of Fy isomer, two parts of a isomer, and one part of isomer.

Lower aliphatic alcohols, at or about room temperature, have a relatively high solubility for the gamma isomer; and, accordingly, when employing only enough solvent to dissolve the gamma isomer, the resulting benzene hexachloride:solvent slurry is excessively thick for pumping, eentrifuging and otherwise processing with known process equipment. For this reason, it is imperative that the extraction process be carriedy out at relatively low temperatures, below about 15 C. and preferably below about 0 C., wherein the solubility in the solvent is substantially decreased. `In addition, when attempting to carry out an extraction in accordance with prior methods, I have now found that there is but a single benzene hexachloride to solvent weight ratio for any one temperature which will provide optimum extraction conditions to give both a high yield and high purity. Thus, a low temperature of operation must be so selected as to permit both efcient operation and practical slurry compositions which may be processed with known process equipment.

However, such low temperature operation necessitates the use of expensive refrigeration equipment, increases operational costs, and renders the exacting control re quired for efficient operation dilcult to achieve. These a ICC 2 factors, in practice, must be balanced against the advantages of refrigerated operation noted above. It has been found that the extraction must normally he carried out at a maximum temperature of C.

Crystallization and separation of a high gamma isomer product is also diiicult to prior processes due to the viscosity of the slurry, resulting in appreciable degrading of the crystalline produce due to adherence of large quantities of impure mother liquor. To minimize this 0 condition, prior processes were conducted at refrigerated temperatures to reduce the viscosity of the slurry from which the product is separated.

lt is accordingly an object of this invention to provide an improved process for producing an enhanced gamma isomer product from crude BHC.

Another object is to provide an improved extraction and crystallization process of the above type wherein an optimum purity product can be obtained in exceedingly high yields over a Wide range of temperature conditions.

Another object is to provide a process in which the crude BHC can be extracted with a wide vrange of solvent to BHC weight ratios so as to allow easy and eiicient handling of the resulting slurry.

Another object is to provide the process in which an exceedingly high purity product can be obtained using a process in which the degree of concentration of the extract solution and the final crystallization temperature is less critical than in prior processes.

Other objects and advantages of the present invention will become apparent as the description proceeds.

lt has now been found that the use of aqueous methanol as the solvent in both the extraction and crystallization steps materially improves the yields and processability in the extraction step and permits the recovery of substantially higher purity products in correspondingly good yields in the crystallization step. The presence of water in the methanol has been found to give greater flexibility to the process, permitting the use of a wide variety of solvent to BHC weight ratios (slurry compositions) for essentially any desired temperature of extrae tion and reduces the criticality of both the degree of super-saturation of the extract solution (concentration of the solution) and crystallization temperature on the product purity and yield of the Valuable gamma isomer from the crude mixture.

in general, the process comprises extracting crude BHC with a limited quantity of aqueous methanol, suicient to dissolve essentially all of the gamma BHC isomer while leaving a relatively large quantity of the BHC undissolved. This is preferably carried out in a suitable vessel by slurrying the BHC with the aqueous methanol for a suilicient period to permit essentially equilibrium conditions. During this extraction, the slurry is preferably agitated to aid solvation of the gamma BHC isomer. Following extraction, the liquid (gamma isomer extract) land solid phases are separated, and the extract is then supersaturated to effect crystallization. This is accomplished at least in part by the addition of water to the extract, and usually by also removing part of the methanol. After this concentration, the water content is adjusted in accordance with this invention, discussed more completely below, and the gamma BHC is per mitted to crystallize. This enhanced purity product is then separated from the crystallizer mother liquor and7 v if desired, can be further purified by one or more re- 3 tration of the extract (by removal of methanol and some water), will automatically give the preferred watermethanol ratio for the crystallization operation. However, generally, it is necessary to add additional water to the concentrated extract, prior to crystallization of the desired gamma isomer product.

The quantity of water to be employed in the methanol in the extraction operation is dependent upon the quantity of gamma isomer in the crude mixture to be extracted, the methanol to BHC weight ratio and the temperature of the extraction operation. Normally the extracting solution should contain between 6 and 16 percent by weight of water, although it is preferred in most operations to employ between about 8 and 14 percent. Within this range, it is necessary to employ from 0.5-6 parts of methanol per part of BHC. For optimum resuits, the water concentration must be correlated with the methanol-BHC ratio, the water concentration increasing (within the range noted) essentially directly with increases in the methanol-BHC ratio, also in the range noted.

The range of water concentration given above, i. e., 616 percent is critical and surprisingly effective since a minimum gamma BHC loss is obtained in this range due to solvent disproportionation of the mother liquor which adheres to the cake during separation. This is shown graphically in the figure.

A more detailed correlation of the quantity of water to be employed with different methanol to BHC ratios and at different temperatures are given in the following formula:

P=a log R-b wherein P is the weight percent of water in the methanol, a is a number having a value of about 23, R is the Weight ratio of methanol to crude BHC and b is a number having a value between -10 and 15 and preferably between 0.5 and 1.5 at 30 C. The range of the value of a is independent of temperature.

The value of b for optimum results should vary in accordance with the temperature in C. as given by the following formula:

wherein 1230 is the value at 30 (between -10 and 15) and t is the actual temperature of extraction.

In the crystallization step, the percent water preferably should be between about 5 and 20 percent by weight of water when employing methanol to BHC ratios between about 1.5 to 1 to about 2 to 1. Within these ranges, optimum results are obtained when these variables are correlated in essentially direct relationship, i. e., employing the lower water concentrations with the lower methanol-BHC weight ratios.

The crystallization is generally carried out at a temperature of C. to 40 C., preferably within the range of about 20 to 35 C. For economic reasons, it is normally preferred to conduct the crystallization at about room temperature.

The time of crystallization required depends primarily on the degree of concentration of the extract solution and the quantity of water employed. In general, shorter crystallization times are preferred when using the higher water concentrations. In general, the crystallization time can be between about minutes to ane hour, preferably of the order of to 25 minutes.

During crystallization, it is normally preferred to employ agitation to increase the rate of crystallization of the valuable gamma isomer. The degree of crystallization is not critical but effects somewhat the particle size of the crystals. In general, the higher the degree of agitation, the smaller the crystal size of the product obtained.

The high gamma benzene hexachloride product, as well as the low gamma extracted cake, can be separated by any of the well known means such as decantation or Example I A mixture of BHC isomers (20 parts) having the following isomer distribution: 65 percent; 8 percent; fy, 13 percent; 10 percent; e, less than 1 percent and the remainder heptachlorocyclohexanes and other impurities was treated at 30 C. with 100 parts of methanol. Suffcient water was added to this solution to give a 12.7 percent water-in-methanol extract. After separation of the liquid and solid fractions, the ltrate contained 15 percent water-in-methanol and 5.9 parts of .BHC having 38 percent gamma isomer purity. Approximately 90 percent of the gamma isomer was recovered in the filtrate. The ltrate was then saturated by removal of a quantity of the methanol at a temperature of about 65 C. to give a methanol to BHC ratio of 1.7 to 1. The water concentration in the mixture was then adjusted to 15 percent. This mixture was then cooled to a temperature of 15 C. in a period of between 15 to 30 minutes. Nine and one-tenth (9.1) parts of crystallized product was obtained having an 85 percent gamma isomer purity. This represents an 82 percent yield of. the gamma isomer based on the gamma isomer content in the extract solution.

Example II Example I was repeated except that the solids from the extract was recovered and redissolved in anhydrous methanol and thereafter crystallized at the same tem- Example III Example II was repeated except that the extract solution contained 9.7 percent water and the methanol:BHC ratio was 1.46z1. In this example, an 82 percent purity product was obtained in 83 percent yield.

Example IV Example III was repeated except that no water was employed and the yield of 83 percent gamma isomer product was reduced to only 42 percent of the gamma isomer content in the extract solution.

Example V Example I was repeated except that the extract solution contained only 6 percent: water prior to crystallization and the methanol to BHC ratio was 1.17: l. In this example, an 85 percent gamma isomer purity product was obtained in a yield of 82 percent.

Example VI Example V was repeated except that no water was employed in the extract solution and the product (S4 percent purity) was obtained in only 55 percent yield.

Example VII Example I was repeated except that the extract solution contained 9 percent water and the methanolzBHC ratio was 1:1. The product had a purity of 80 percent and was obtained in percent yields based on the gamma isomer in the extract solution.

Example VIII Example VII was repeated except that no water was employed and the product was obtained in only 36 percent yield.

Example IX Example I was repeated except that the extract solution contained 8 percent water and the methanolzBI-IC ratio was 1.32: l. The product had a purity of 84 percent and was obtained in 70 percent yield based on the crystal lizable gamma isomer in the extract solution.

Example X Example IX was repeated except that no water was employed in the extract solution. The product contained only 80 percent gamma isomer and was only obtained in 40 percent yield.

yExample XI Example I was repeated except that the extract solution contained 8.5 percent water and the methanokEHC ratio was 0.66: l. A product containing 85 percent gamma isomer was obtained in 51 percent yield.

Example XII IExample XI was repeated except that no Water was contained in the extract solution. The product contained 85 percent purity but was only obtained in 10 percent yield.

The following examples illustrate variations in the extraction process in accordance with the present invention.

Example XIII A mixture of BHC isomers (50 parts) having a similar isomer distribution to that of Example I was treated at 30 C. with 100 parts of methanol, followed by addition of a sucient quantity of water to provide a 6 percent aqueous filtrate solution, on the solid-free basis. This mixture was thereupon stirred until equilibrium was attained. The ltrate, after separation from the solids, contained 16.28 parts of benzene hexachloride having 35 percent gamma isomer, corresponding to 89 percent of the total gamma isomer in the einde product.

Example XIV A mixture of benzene hexachloride isomers (25 parts), having essentially the same isomer distribution as that of Example I, was treated at 30 C. with 100 parts of methanol containing in addition suicient Water to give an 11.5 percent water-in-methanol in the extract and, after filtration, a 13 percent water-in-methanol filtrate solution. The

extract and solids were stirred until system equilibrium was attained. The yield of the gamma isomer in the filtrate, based on the original mixture, was 93 percent.

Example XVI A mixture of benzene hexachloride isomers (20 parts), having essentially the same isomer distribution as that of Example I, was treated at 30 C. with 100 parts of methanol. Suiiicient water was added to this solution to give a 12.7 percent water-inr-methanol extract. After separation o1 the liquid and solid fraction, the filtrate contained 15 percent water-in-methanol and 5.9 parts of benzene hexachloride having a 38.7 percent gamma isomer purity. Approximately percent of the gamma isomer was recovered in the filtrate.

.I claim:

l. A process for producing an enhanced gamma benzene hexachloride product from a crude mixture of benzene hexachloride isomers in which the gamma isomer is recovered in a high purity and yield, comprising extracting said crude benzene hexachloride with aqueous methanol in a quantity only suiiicient to dissolve essentially all of the gamma benzene hexachloride, thereby leaving undissolved a substantial quantity of the crude benzene hexachloride, separating the liquid extract from the undissolved solids, concentrating said extract by removing a quantity of the methanol therefrom, and thereafter cooling said extract to crystallize a product containing an enhanced proportion of gamma benzene hexachloride from said concentrated extract, the aqueous methanol extracting solution containing between about 6 and 16 percent by Weight of water and containing between 1/2 part and 6 parts of methanol per part of crude benzene hexachloride, the aqueous methanol concentrated extract solution containing between about 5 and 16 percent by weight of Water and containing from l part to 2 parts of methanol per part of benzene hexachloride, the crystalli- Zation temperature being between 0 and 40 degrees C., and the Water, methanol and crude benzene hexachloride Weight ratios during the extraction being such that References Cited in the le of this patent UNITED STATES PATENTS Burrage et al May 22, 1951 Burrage et al. July 15, 1952 

1. A PROCESS FOR PRODUCING AN ENCHANCED GAMMA BENZENE HEXACHLORIDE PRODUCT FROM A CRUDE MIXTURE OF BENZENE HEXACHLORIDE ISOMERS IN WHICH THE GAMMA ISOMER IS RECOVERED IN A HIGH PURITY AND YIELD, COMPRISING EXTRACTING SAID CRUDE BENZENE HEXACHLORIDE WITH AQUEOUS METHANOL IN A QUANTITY ONLY SUFFICIENT TO DISSOLVE ESSENTIALLY ALL OF THE GAMMA BENZENE HEXACHLORIDE, THEREBY LEAVING UNDISSOLVED A SUBSTANTIAL QUANTITY OF THE CRUDE BENZENE HEXACHLORIDE, SEPARATING THE LIQUID EXTRACT FROM THE UNDISSOLVED SOLIDS, CONCENTRATING SAID EXTRACT BY REMOVING A QUANTITY OF THE METHANOL THEREFROM, AND THEREAFTER COOLING SAID EXTRACT TO CRYSTALIZE A PRODUCT CONTAINING AN ENCHANCED PROPORTION OF GAMMA BENZENE HEXACHLORIDE FROM SAID CONCENTRATED EXTRACT, THE AQUEOUS METHANOL EXTRACTING SOLUTION CONTAINING BETWEEN ABOUT 6 AND 16 PERCENT BY WEIGHT OF WATER AND CONTAINING BETWEEN 1/2 PART AND 6 PARTS OF METHANOL PER PART OF CRUDE BENZENE HEXACHLORIDE, THE AQUEOUS METHANOL CONCENTRATED EXTRACT SOLUTION CONTAINING BETWEEN ABOUT 5 AND 16 PERCENT BY WEIGHT OF WATER AND CONTAINING FROM 1 PART TO 2 PARTS OF METHANOL PER PART OF BENZENE HEXACHLORIDE, THE CRYSTALLIZATION TEMPERATURE BEING BETWEEN 0 AND 40 DEGREES C., AND THE WATER, METHANOL AND CRUDE BENZENE HEXACHLORIDE WEIGHT RATIOS DURING THE EXTRACTION BEING SUCH THAT 